The present invention relates to a device for closing off large pipelines, in particular hot-gas pipelines. Such a device is disclosed in Federal Republic of Germany Patent No. 22 44 972. In that device, a plurality of pivoted flaps are arranged parallel to one another within a frame, and each of the flap shafts has, at its end, a straight double-armed swing lever on their arms upon which rigid connecting rods act. A drive actuates these connecting rods, which swing and/or displace the swing levers, and thus also the pivoted flaps. Each swing lever is pivotally connected through two short connecting pieces to a hub piece which is fastened on the end of a flap shaft. This articulated connection allows for the swinging or turning movement of the lever to be transmitted directly to the pivoted flaps. Additionally, thermal expansion of the frame, which enlarges the distance between the flap shafts, does not lead to undesired tensile stresses in the connecting rods because the swing levers avoid extension in length of the frame by tilting away. However, this tiling of the swing levers is limited by the length of the short connecting pieces. In particular, if pivoted flaps of widths of at least about 2 meters are used and/or several pivoted flaps are used which are parallel to one another, thermal expansion in the frame, which occurs at temperatures of, for example about 500.degree. to about 600.degree. C., can no longer be compensated for by the tilting away of the levers. Enormous tensile forces then occur in the connecting rods which possibly leads to damage to the connecting rods, the articulated connections, and the levers.
Lengthening of the connecting pieces between the swing lever and the hub piece on the flap shaft would result in an increase in the compensatory movement but it would also cause considerable bending and torsional forces to occur in these connecting pieces. These forces can barely be controlled, even if expensive stiffenings and ribs are used. Such a lengthening of the connecting pieces is also particularly disadvantageous because a considerable loss of structural height must be tolerated. Should the above-described disadvantages be tolerable, frequently only very little installation space is available in large pipelines so that a lengthening of the connecting pieces, can frequently not be accomplished or at least one of a sufficient degree.